Electric resistance furnace



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ELECTRIC RESISTANCE FURNACE Filed Jan. 18, 1945 7 sheets-sheet s l Inveno 2: EaneFPoZafzd June 7 1949- F. F. POLAND 2,472,613

ELECTRIC RESISTANCE FURNACE Filed Jan. 18, 1945 l 7 sheetssneet 4 m Y 0 a uys,

June 7, 1949. F. F. POLAND ELECTRIC RESISTANCE FURNACE 7 Sheets-Sheet 5 Filed Jan. 18, 1945 17V/vena?.- anc FPoZaw. By LA7/94m minfin/mf -z/ya June 7', 1949. F. F. POLAND 2,472,613

' ELECTRIC RESISTANCE'FURNACE '7 Sheets-Sheet 6 Filed Jan. 18. 1945 F. F. POLAND ELECTRIC RESISTANCE FURNACE June 7, 1949.

'1 shuts-sheet '7 Filed Jan. 18. 1945l Patented June 7, 1949 UNITED STATES PATENT OFFICE ELECTRIC RESISTANCE FURNACE Application January 18, 1945, Serial No. 573,337

. 14 Claims. 1

My invention relates to electric furnaces of the resistance type. It has for its object an improved support for the resistance elements, and in this respect constitutes an improvement in the electric furnace forming the subject matter of my pending application Serial Number 536,580, filed May 20, 1944.

The invention -will be best understood from the following description when 'read in the light of the accompanying' drawings of several embodiments of the invention, the scope of which latter will be more particularly pointed o ut in the appended claims.

In the drawings:

Fig. 1 is a section on the line I-I of Fig. 2 of an electric furnace according to the invention;

Figs. 2, 3 and 4 are, respectively, sections on the lines- 2-2, 3-3 and 4-4 of Fig. 1, Fig. 4 being a fragmentary section on an enlarged scale;

Fig. 5 is a section on the line 5-5 of Fig. 4;

Fig. 6 is a fragmentary plan of the parts according to Fig. 4;

Fig. 7 is a section on the line 'I-'l of Fig. 4;

Fig. 8 is a fragmentary section on the line 8 8 of Fig. 3 on an enlarged scale;

Fig. 9 is an elevation of parts shown by Fig. 8;

Fig. 10 illustrates a modified form of the invention corresponding to a fragmentary section on the line 3-3 ofFig. 1;

Fig. 11 is an elevation of one of the resistor bars according to Fig. 10;

Fig. 12 is a section on the line I2-I2 of Fig. 11;

Fig. 13 is a fragmentary section, on an enlarged scale, on the line I3-I3 of Fig. 10;

Fig. 14 is a'section on the line I4-I4 of Fig. 13; and

Fig. 15 is a plan of the parts according to Figs. 13 and 14.

The furnace illustrated, except for the resistors, resistor supports and associated parts, is substantially identical with that illustrated in applicantss pending application referred to, certain parts however being shown more or less diagrammatically for simplification of illustration. The furnace will therefore not be described with any more particularity than necessary for an understanding of the present improvement.

Referring particularly to Figs. 1 to 9, the furnace comprises a body portion having a metal casing I, and a cover having a metal casing 3. Carried by the four lateral walls of the casing I adjacent its upper edge are angle-irons 5 extending continuously about said walls. Carried by these angle-irons are angle-iron-like members having lower horizontal webs 'I and upwardly projecting webs 9, and carried by the webs 1 in spaced relation to the Webs 9 are upwardly pro` jectlng partitions II, the webs 1 and 9 and the partitions II also extending continuously about 5 the four lateral Walls of the casing I. Carried by the foury lateral walls of the casing 3 are I-beams I3, and carried by the outermost flanges of the latter are elongated vertical plates I5 in spaced relation to those Walls. At their upper edges the plates I5 carry elongated horizontal plates I1, the latter carrying downwardly projecting partitions I9, the I-beams I3, plates I5 and I1, and partitions I9 extending continuously around the four lateral walls of the casing 3. When the cover is positioned on the body of the furnace, as illustrated in Fig. 1, the partitions I9 project into the spaces between the Webs 9 and partitions II, while the plates I5 project into the spaces between the partitions II and the lateral Walls of the casing I. This intertting of the parts forms a labyrinth seal which may be lled with sealing material, for example oil, up to adjacent the level of the top edge of the lateral walls of the casing I, the parts of this seal including the casing walls, anglefirons 5 and I-beams I3 preferably being secured together by welding to form air tight joints between them.

Interiorly of the casing I are provided massive carbon blocks 2I forming the oor of the furnace chamber, and on these` blocks rest the massive carbon blocks 23 forming the end walls of the furnace chamber, and the massive carbon blocks 25 forming the side walls thereof. Between the carbon blocks 2I and the bottom wall of the casing I,'and between the blocks 23 and 25 and the side -Walls of that casing, is placed refractory material 21 and 29 respectively, this material preferably being that illustrated in the above mentioned pending application and being merely diagrammatically illustrated in the present application.

As illustrated, the blocks 23 and 25 forming the lateral Walls of the furnace chamber are formed near their upper edges to provide shoulders 3I on which rest a row of removable graphite slabs 33 forming the roof of the furnace chamber. As best illustrated in Fig. 14, the adjacent longitudinal edges of these slabs are preferably shiplapped so as to provide, between their opposed vertical faces, spaces 35 for preventing stresses on the slabs due to expansion or contraction of the furnace Walls, while forming a tight seal between adjacent slabs because their abutting horizontal surfaces 31 are in contact.

As illustrated, for charging the furnace chamber with molten metal is shown a conduit 39 having a spout 4l projecting into the cavity 43 of a cup-shaped member 45 within the furnace chamber, the end of the spout being below the upper edge of the member 45 for causing liquid metal to seal the end of the spout` Metal will now over the upper edge of the member 45 to fill Ithe furnace chamber with metal, say to the level L. For discharging metal from the furnace chamber is shown a conduit 41 normally closed by a screw-threaded plug 49 which may be removed by use of a key wrench inserted in the conduit from its outer end after the removable cover plate 5I is removed. For discharging vaporsfrom the furnace chamber is provided a conduit 52 extending through one of the lateral walls of the furnace.

As illustrated, within the casing 3 of the cover of the furnace is an arch-like structure lformed of the massive carbon blocks 59, the intermediate slabs being keyed together at 55 and the end slabs resting on the wedge-shaped carbon blocks 51, which latter are supported, when the cover is lifted, by elongated angle-irons 59 on which -they rest, these angle-irons being welded to the lateral walls of the casing 3 adjacent their lower edges and extending entirely about said walls. As shown, the blocks 53 are so shaped as to provide a recess til between the upper walls of the furnace chamber roof slabs 93 and the lower walls 63 of said blocks. Between the slabs or blocks 53 and 51 and the top wall of the casing il are layers y65 of refractory material, preferably those illustrated in the above mentioned application, the layers being merely diagrammatically shown in the accompanying drawings.

As illustrated, the resistors are in the form of elongated bars t1 of heat refractory electric conductiile material, preferably graphite. These bars extend transversely across the upper portion of the furnace chamber. As shown, they are Iprovided with screw-threaded end portions t9 of slightly enlarged diameter. These end portions extend through openings 1i in connector plates 13 of the same material as the resistors. On the screw-threaded end portions t9 at opposite ends of the connector plates are shown, screw-threaded nuts or collars 15 between which the connector plates are clamped. As shown, the openings 1i (see Fig. 5) are slightly elongated in the direction of the length of the furnace chamber to permit the resistors to slide relative to the connector plates when the assembly formed by the series of resistors and connector lplates expands and contracts dueto temperature changes. It vwill be understood in this connection, that a1- though the -collars 15 may be of relatively large area and tightly clamped against the connector plates', the two may slide relative to each other fairly easily because graphite of which these parts yare formed has good lubricating properlties especially when heated to high temperatures.

As illustrated, each end resistor bar of the series is connected by a coupling sleeve 19 to a rigid extension 8i, preferably formed of graphite, the adjacent ends of the resistor bar and extension being screw-threaded into this coupling. Each extension 8| extends through an opening 93 in the lateral wall of the furnace chamber to the exterior of the casing l. As shown in Fig. 8, the projecting end of the extension is screw-threaded and is received in the screw-threaded socket portion 85 of the base portion of a terminal lug, which latter is preferably formed of copper. As shown, the terminal lug has a screw-threaded .4 small diameter portion 81 to which may be attached the cable for energizing the resistors.

Carried by the portion 81 of each terminal lug is shown a plate l89 of heat refractory electric insulating material, preferably material of the type employed for panels of radio receivers and like pur-poses, this plate resting against the shoulder portion 9| of the terminal lug, and being secured to the latt'er by the washer 93 and nut 95 screwthreaded on the terminal lug portion 81. As shown, the plate 89 adjacent its upper edge is formed with an opening 91 which receives a hook 99 at one end of a turnbuckle indicated in its entirety at lill, the opposite end of the turnbuckle having a hook |03 received in an opening |95 of a lug |01 secured as by welding to the web or plate 9 of the labyrinth seal hereinbefore described. By this construction the 4terminal lugs and resistor extensions 8| are supported, and undue strain that might be placed upon them by the cables attached to the terminal lugs is prevented.

For sealing the joint between the walls of the furnace and each resistor extension 8| the same vis shown as packed with a yieldable layer |09 of asbestos or other yieldable heat refractory electricv insulating material, a layer iii of like material preferably being positioned between the end of the socket portion of the terminal lug and the wall of the casing l, the layer iii being :placed within `an annular retaining collar H3 secured as by welding to the casing i. These packing layers being yieldable, the extensions 8| despite the layers, remain operatively in spaced relation to the surrounding Walls of the openings 59 in the sense that relative movement between the extensionsand such walls transversely and longitudinally of the extensions, and .tilting of the extensions in any direction, are not prevented. The sus-pension at the end of the extension provided bythe turnbuckle idi and associated parts readily permits such movement. For preventing any excess longitudinal movement of the extensions relative to the walls of the furnace, beyond that caused by the expansion of the series connected resistors or of said walls, the lower portion of each plate te is shown as provided with an opening H5 through which loosely extends la rigid rod lill, the latter at one end being rigidly'secured to the casing i as by welding. As shown, this rod at its free end is screw-threaded and adjustably carries a pair of nuts i i9 respectively positioned at opposite sides of the plate 39. Each nut is shown as positioned in spaced relation to the adjacent surface of the plate, which spacing in conjunction 'with the loose t of the rod in the opening i i5 will permit longitudinal, transverse and tilting movement of the associated extension 9i relative to the furnace walls.

As illustrated in Figs. 1 to 7, for supporting the series connected resistors interiorly of the furnace, the connector plates 13 are shown as slidably resting upon bars 512| preferably formed of graphite, .the lower edges of the resistor plates being notched, as shown 'at |23 (Fig. 5), for receiving these bars. Screw-threaded into the bars i2! are shown vertically extending rods i '25,y preferably formed of graphite, which are positioned at opposite sides of the connector plates in spaced relation thereto. These rods extend upwardly through openings |21 in the slabs 33 forming the roof of the furnace chamber into the recess -Bl of the blocks 59 of the cover of the furnace. On the upper ends of the rods are screw-threaded collars or nuts |29, also preferably formed of graphite. Loosely surrounding each rod is shown a block |3| which rests upon the upper side of the slab 33, this block -preferably being formed of porous carbon which is extremely heat refractory and a relatively poor conductor of heat. Positioned on each block |3| is shown a block |33 of heat refractory electric insulating material on which the nuts |29 rest, these last mentioned blocks preferably being formed of sintered aluminum oxide A120: of high purity, say -about 99.5% pure, such as the material sold under the trade name Alfrax.

Applicant has experienced great difficulty in providing an electric insulating resistor support that will withstand the high temperature conditions present in a furnace of the type described, which temperature commonly may be as high as 2800 to 3800 F. Although electric insulating material described in connection with the insulating block |33 is about the most heat refractory one commercially available, it may under some conditions soften vand fail if placed interiorly of the furnace chamber. By placing it at the exterior of the furnace chamber as above described, where the temperatures are lower than in the furnace chamber, and placing between it and the walls of the furnace a block of porous carbon, which as above explained is highly heat refractory, and, as compared to solid carbon or graphite, a relatively poor heat conductor, the electric insulating blocks |33 are kept relatively cool, as cornpared to the temperatures mentioned, and will effectively resist softening or other deterioration. At the same time the construction described permits the resistor connector plates 13 to rest upon graphite surfaces which, las above explained, have very good lubricating qualities at high temperature, so that the parts may move readily relative to each other due to the expansion and contraction caused by changes in temperature.

For insulating the roof of the furnace chamber;

' there is shown a mass |35 of broken up charcoal heaped on the roof slabs 33 of the furnace chamber, which mass substantially lls the recess 6| in the cover of lthe furnace chamber. For preventing this charcoal from contacting with the suspension rods |25, nuts |29 and blocks |3| and short circuiting them to the graphite roof slabs 33, the upperends of said rods are shown as surrounded by Walls formed of blocks |31 of carbon or other suitable highly heat refractory material. these blocks removably resting upon the roof slabs 33.

In the modification shown lby Figs. l to 15, the resistors |39, which preferably are formed of graphite, are shown as generally square in cross-section and longitudinally grooved adjacent their lower corners to form surfaces III and |43 which increase the heat radiating capacity of the resistors particularly downward toward the pool of metal in the furnace. These resistors are shown as provided with the cylindrical screw-threaded extensions |45 at 'each of opposite ends thereof, which extensions extend through openings |41 in graphite connector plates |49. As shown, screw-threaded on the extensions at opposite sides of the connector plates are the nuts or collars 15 like those hereinbefore described in connection with Figs. 1 to 9.

As shown in Fig. 10, the resistors |39 are placed so close together that the suspended .rods |25 employed in the construction according'tc Figs. 4 and 5 cannot be placed between the collars 15, with the result-that the construction shown by these two last mentioned figures cannot be employed in connection with the resistors spaced as shown in Fig. 10 without materially shortening the resistors. Consequently, as shown in Figs. l0, 13 and 14, there is employed in connection with each connector plate but one suspended rod |5|, which rod, like the suspended rods heretofore described, preferably is formed of graphite. As shown (see Figs. 13 and 14), the lower end of each rod |5| is screw-threaded into an open- -ing in a bar |53, which latter provides the rod with a laterally projecting lug on which the associated connected plate slidably rests. In this construction, because of the close spacing of the nuts or c'ollars 15, the lower edge of the connector plate cannot be notched as shown in Figs. 4 and 5,- and to provide clearance for the bar |53 the adjacent shelf |55 of the furnace wall is recessed as shown at |51.

Each suspension rod, as shown, extends through an opening |59 in a roof slab 33 of the furnace chamber into the recess 5| formed by the blocks 53 of the cover for the furnace. For supportingr each suspension rod on the adjacent roof slab collar or nut |6| is screw-threaded on the end of the upper rod, and interposed between this nut and the roof slab are an electric insulating block |63, of the same material as the block |33 hereinbefore described, and a block |65 of porous carbon, the latter resting on the roof slab. Like the construction according to Figs. 1 to 10, surrounding the upper end of each suspension rod is a wall formed of blocks |31 for isolating that end of the rod from the charcoal mass |35.

In assembling the series connected resistors according to Figs. 1 to 9 the same, prior to positioning the roof slabs 33, may be built up .inside the furnace chamber with the coupling sleeves 19 and connector plates 13 supported upon wooden blocks resting upon the shelf |55 of the furnace chamber walls, and with the suspension rods |25 assembled with the bars |2| and embracing the connector plates, the bars |2| also resting upon this shelf. The resistor extensions 8| may then be inserted through the openings 83 in the furnace walls and screwed into the 1 coupling sleeves 19, whereupon the terminal lugs and associated partsA may be assembled with said extensions and connected by means of the turnbuckles ||l| to the casing. The roof slabs 33 may thenV be progressively laid in position starting from one end of the furnace chamber, the slabs having the openings for receiving the suspended rods being positioned with said rods extendingthrough said openings. As the slabs are progessively positioned the blocks |3| and |33 and nuts |29 may be placed on the extension rods and the nuts screwed up, and the wooden blocks above referred to may be progressively removed. In disassembling the parts the wooden blocks may be placed in position as the slabs 33 are progessively removed. The same procedurel may be followed in assembling and disassembling the parts according to Figs. 10 to 15.

It will be understood that in the appended claims by the words heat refractory carbonaceous material is meant materials of construe'- tion commerically and in the furnace are known as carbon and graphite It will be understood that within the scope of the appended claims wide deviations may be made from the forms of the invention described `without departing from the spirit of the invention.

I claim:

1. An electric furnace having, in combination, means forming a furnace chamber enclosed by relatively fixed lateral walls and having a roof defining the top of said chamber, said roof comprising substantially abutting slabs of heat reroof, for suspending said row of resistors fromsaid roof, said slabs having openings through which said spaced means extend in out of electrical contacting relation with the Walls of such openings, bodies of heat refractory porous carbon of less heat conductivity than the material of said slabs resting on the latter at the upper sides thereof in out of electrical contacting relation with said spaced means, and heat refractory electric insulating means carried by said bodies in spaced relation to said slabs for operatively supporting said spaced means on said slabs.

2. An electric furnace having, in combination. means forming a furnace chamber having a roof, which latter comprises a wall of heat refractory carbonaceous material defining the top of said chamber, electric heating resistors in said chamber beneath said roof, means suspending said resistors from said roof comprising elongated members of heat refractory carbonaceous material extending through openings formed in said wall to the upper side of the latter, and heat refractory electric' insulating means operatively carried by said wall at the upper side thereof for supporting said members on said wall.

3. An electric furnace according to claim 2 in which the means for suspending the resistors from the roof is formed of graphite and slidably supports them.

4. An electric furnace according to claim 2 in which a body of heat refractory material, of relatively poor heat conductivity as compared to the wall defining the top of the furnace chamber, rests on the top of said wall and is interposed between it and the electric insulating means, the latter resting on said body.

5. An electric furnace according to claim 2 in which the wall defining the top of the furnace chamber is formed of graphite, and in which a body of heat refractory porous carbon, of relatively poor heat conductivity compared to graphite, rests on the top of said wall and is interposed between it and the electric insulating means, the latter resting on said body.

6. An electric furnace having, in combination, means forming a furnace chamber having a roof, which latter comprises a wall of heat refractory carbonaceous material defining the top of said chamber, electric heating resistor means in said chamber positioned beneath said roof comprising a row of laterally spaced bars, members formed of heat refractory carbonaceous material connecting adjacent ends of said bars for series current oW through them, means suspended from said wall supporting said members, said last mentioned means being formed of heat refractory carbonaceous material comprising an elongated part extending through an opening formed in said wall to the upper side thereof, and heat refractory electric insulating means operatively carried by said wall at the upper side thereof for supporting said part on said wall.

7. An electric furnace according to claim 6 in which a body of heat refractory material, of relatively poor conductivity as compared to the wall defining the top of the furnace chamber, rests on the top of said wall and is interposed between it and the electric insulating means, the latter resting on said body.

8. An electric furnace having, in combination, means forming a furnace chamber enclosed by relatively fixed lateral walls and having a roof defining the top of said chamber, said roof comprising a plurality of substantially abutting slabs supported for removal from above said chamber, a row of laterally spaced elongated heating resistors in said chamber beneath said-roof disposed in parallel relation to said slabs, members connecting adjacent ends of said resistors for series ow of current through them; and a plurality of independently removable spaced means for supporting said resistors from said roof severally carried by single slabs of said plurality of slabs, said plurality of spaced means comprising vertical rods extending through openings in said' slabs from below to above said roof, which rods are in out of electrical contacting relation with the walls of such openings andv carry laterally extending parts below said roof, on which parts said members slidably rest, and which rods are operatively supported above said roof by heat refractory electric insulating parts operatively carried by said slabs at the upper sides thereof for suspending said rods from said slabs.

9. An electric furnace having, in combination, means forming a furnace chamber, means forming a roof for said chamber comprising removably supported slabs dening the top of said chamber, a row of laterally spaced resistor bars' positioned in said chamber beneath said roof, members connecting adjacent ends of said bars for series current flow through them, means for supporting said members comprising pairs of vertically extending rods suspended from different slabs, the rods of each pair lying at opposite sides of the adjacent member and carrying a bridge piece on which said member rests.

10. An electric furnace having, in combination, means forming a casing lined with refractory material to form a furnace chamber, electric heating resistance means movably supported within said chamber, said last mentioned means having a rigid extension projecting through an opening formed in such lining and casing operatively in spaced relation to the walls of such opening, and means carried by said casing and connected to the portion of said extension at the exterior of said casing for suspending said extension from said casing for longitudinal, lateral and tilting movements thereof.

11. An electric furnace having, in combination, means forming a. furnace chamber, means forming a roof for said chamber, a row of laterally spaced resistor bars positioned in said chamber beneath said roof, members for connecting adjacent ends of said bars for series current ilow through them, which members are provided with enlarged openings through whibh the end portions of said bars extend, means carried by said bars lslidably contacting with said members for establishing and maintaining electrical communication between them while permitting said bars to move laterally relative to said members, and means for suspending said bars and members from said rcof.

12. An electric furnace having, in combination, means forming a furnace chamber, means forming a roof for said chamber comprising removably supported slabs dening the top of said chamber, a row of laterally spaced resistor bars positioned in said chamber beneath said roof, members for connecting adjacent ends of said bars for series current flow through them, which members are provided with enlarged openings through which the end portions of said bars extend, means carried by said bars slidably contacting with said members for establishing and maintaining electrical communication between them while permitting said bars to move laterally relative to said members, and means for suspending said bars and member-s from said roof.

13. An electric furnace having, in combination, means forming a furnace chamber having a lateral wall and a roof, electric heating resistance means in said chamber beneath said roof, means for slidably supporting said resistance means from said roof, said resistance means having an extension projecting into an opening formed in said lateral wall with said extension in laterally spaced relation to the walls of said opening, and a heat refractory packing 2 for said opening in surrounding relation to said extension, which packing is yieldable for permitting movement of said extension laterally relative to the walls of said opening.

14. An electric furnace having, in combina- 3W i0 tion, means forming a furnace chamber having lateral walls and a roof, electric heating resistance means in said chamber beneath said roof and slidably suspended therefrom comprising spacedresistor bars connected for series ow of current, said resistance means having spaced extensions projecting into separate spaced openings formed in said lateral Walls with .said extensions in laterally spaced relation to the Walls of said openings, and a heat refractory packing for each of said openings in surrounding relation to said extensions, which packings are yieldable for permitting movement of said extensions laterally relative to the Walls of said openings.

FRANK F. POLAND.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,346,854 Smalley July 20, 1920 1,413,678 Moffat Apr. 25, 1922 1,472,137 Reid Oct. 30, 1923 1,472,139 Reid Oct. 30, 1923 1,690,273 Cope Nov. 6, 1928 1,719,888 Ipsen et al. July 9, 1929 2,202,874 Smalley July 4, 1940 

